[Fix] Fix the dispatcher() stuck caused by availablePermitsCh

[Gleiphir2769]

Motivation

The availablePermitsCh may cause the dispatcher stuck.

pulsar-client-go/pulsar/consumer_partition.go

Lines 1096 to 1109 in 0b0720a

	case messageCh <- nextMessage:
	// allow this message to be garbage collected
	messages[0] = nil
	messages = messages[1:]
	pc.availablePermitsCh <- permitsInc
	case pr := <-pc.availablePermitsCh:
	switch pr {
	case permitsInc:
	pc.increasePermitsAndRequestMoreIfNeed()
	case permitsReset:
	pc.availablePermits = 0
	}

For example, if messageCh <- nextMessage continueously selected 10 times, the availablePermitsCh will be filled. The next messageCh <- nextMessage will be stuck forever because pr := <-pc.availablePermitsCh can never be reached.

Modifications

Remove the pc.availablePermitsCh from dispatcher.

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

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This change added tests and can be verified as follows:

[Gleiphir2769]

@RobertIndie @nodece Hi, could you give a review?